The present invention relates generally to enhanced tubes for use in a heat exchanger, and, more specifically, to condenser tubes adapted to have refrigerant flowing internally within the tube and simultaneously having a cooling fluid flowing externally over the same tube, wherein the tubes have fine internal grooves. These tubes may have external fins.
Tubes having integral internal fins have been known for some time as disclosed in U.S. Pat. No. 4,118,944 assigned to the present assignee. However, these tubes generally have large pressure losses due to the height of the fins and a large lead angle between the fins and the axis of the tube.
As disclosed in U.S. Pat. No. 4,044,797 enhanced tubes having grooves with depths between 0.02 and 0.2 millimeters and a mass velocity of 30,300 lb.sub.m /hr-ft.sup.2 provides good heat-transfer, since heat-transfer rates decrease below or above this range of groove depths and pressure losses increase as flow increases. Thus, in order to obtain the high efficiency desired from an internal finned tube it was believed to be necessary to have a fin height greater than 0.02 millimeters and a relatively low mass velocity. Moreover, the typically higher pressure drops of the prior-art tubes were compensated for by an increased surface area due to the larger internal fins, but contained more material per unit length of tube, therefore increasing the cost per unit length of tube.